The present invention relates to a method and apparatus for aseptic moulding of containers of plastic material. As is well known, in an aseptic bottling line there exists a need to sterilize the moulded containers or parisons.
For example, document EP1837037 under the applicant's name proposed an apparatus and a method for chemically sterilizing the containers after the moulding step and before the filling step. However, sterilizing the parisons is preferable to sterilizing the moulded containers since the latter, having a larger surface area, require longer treatment times and, in the case of chemical sterilization, a greater consumption of sterilizing substances (e.g. hydrogen peroxide or peracetic acid).
In this respect, there is envisaged the possibility of sterilizing the parisons before sending them to the heating unit. However, such a solution poses the problem of having to deliver the parisons to the oven cold in order to obtain a correct temperature profile. Moreover, both the oven and the system for handling the parisons must be maintained sterile.
Another solution, proposed by document EP996530, envisages depositing a heat-activatable sterilizing substance (e.g. hydrogen peroxide) on the outer surface of the parisons. The parisons are subsequently conveyed to a heating unit where the sterilization thereof is completed. However, such a solution poses the following problems:                the sterilization process must not interfere with correct pre-blow heating;        the chemical residues deriving from sterilization must be disposed of;        the processing times are lengthened.        
Another solution, represented by document EP1896329, envisages moving the step of chemically sterilizing the parisons to after the heating thereof. However, this solution as well carries with it the disadvantages of using sterilizing chemical agents.
There also exists the possibility of using radiation sources to perform the sterilization, as described in document E22146838. Compared to chemical sterilization, radiation sterilization has the advantage of reducing the operating costs due to the consumption of chemical agents, it resolves the problem of disposing of chemical residues, and it enables the realization of eco-sustainable systems.
It may be noted, moreover, that radiation sterilization envisages the use, alternatively, of:                directly ionizing radiation, such as electrons or other accelerated charged particles;        indirectly ionizing radiation, such as X-rays or γ-rays;        non-ionizing radiation, such as infrared rays, ultraviolet rays or visible light.        
Low-energy directly ionizing radiation allows very high doses (several tens of kiloGrays) to be reached within a short time but has a limited capacity of penetration (only a few micrometers) into PET to be sterilized. On the other hand, indirectly ionizing radiation has a high capacity of penetration (several centimeters) into PET, but requires minutes or hours of time to reach the target sterilizing dose.
Among the prior art solutions, one may also note document FR2907684, in which the parisons are sterilized by means of infrared and ultraviolet rays. In this context, the technical task at the basis of the present invention is to propose a method and apparatus for aseptic moulding of containers of plastic material which overcome the drawbacks of the aforementioned prior art.